Superconducting Qubits: Charge read-out and backaction

For quantum computers to become reality, not only do the qubits have to be carefully engineered to be well isolated during operation time, but this also puts great strain on the measurement setup. We have looked at the backaction from a single-electron transistor (SET), operated both in the normal and in the superconducting state, on a single Cooper-pair box qubit. We have also designed a new read-out setup for a flux qubit using a Cooper-pair transistor that would allow read-out at the flux degeneracy point. In the first case we calculate the mixing time and the influence on the qubit steady-state distribution. We find that the mixing time is larger than typical experimental measurement times, indicating the possibility of single shot read-out. For the steady-state distribution of the qubit, we calculate the Coulomb staircase, finding additional structure due to the noise in the SET.

For the flux qubit we design a read-out scheme involving a quantum flip-flop process, where the measurement outcome results in the presence or absence of an incoherent tunneling process. We estimate read-out and mixing times and find that single shot read-out should be achievable.

BibTeX @book{Käck2004,author={Käck, Andreas},title={Superconducting Qubits: Charge read-out and backaction},isbn={91-7291-556-0},abstract={For quantum computers to become reality, not only do the qubits have to be carefully engineered to be well isolated during operation time, but this also puts great strain on the measurement setup. We have looked at the backaction from a single-electron transistor (SET), operated both in the normal and in the superconducting state, on a single Cooper-pair box qubit. We have also designed a new read-out setup for a flux qubit using a Cooper-pair transistor that would allow read-out at the flux degeneracy point. In the first case we calculate the mixing time and the influence on the qubit steady-state distribution. We find that the mixing time is larger than typical experimental measurement times, indicating the possibility of single shot read-out. For the steady-state distribution of the qubit, we calculate the Coulomb staircase, finding additional structure due to the noise in the SET. <p>For the flux qubit we design a read-out scheme involving a quantum flip-flop process, where the measurement outcome results in the presence or absence of an incoherent tunneling process. We estimate read-out and mixing times and find that single shot read-out should be achievable.},publisher={Institutionen för mikroteknologi och nanovetenskap, Chalmers tekniska högskola,},place={Göteborg},year={2004},series={Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology, no: 13Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, no: 2238},}

RefWorks RT Dissertation/ThesisSR PrintID 4249A1 Käck, AndreasT1 Superconducting Qubits: Charge read-out and backactionYR 2004SN 91-7291-556-0AB For quantum computers to become reality, not only do the qubits have to be carefully engineered to be well isolated during operation time, but this also puts great strain on the measurement setup. We have looked at the backaction from a single-electron transistor (SET), operated both in the normal and in the superconducting state, on a single Cooper-pair box qubit. We have also designed a new read-out setup for a flux qubit using a Cooper-pair transistor that would allow read-out at the flux degeneracy point. In the first case we calculate the mixing time and the influence on the qubit steady-state distribution. We find that the mixing time is larger than typical experimental measurement times, indicating the possibility of single shot read-out. For the steady-state distribution of the qubit, we calculate the Coulomb staircase, finding additional structure due to the noise in the SET. <p>For the flux qubit we design a read-out scheme involving a quantum flip-flop process, where the measurement outcome results in the presence or absence of an incoherent tunneling process. We estimate read-out and mixing times and find that single shot read-out should be achievable.PB Institutionen för mikroteknologi och nanovetenskap, Chalmers tekniska högskola,T3 Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology, no: 13Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, no: 2238LA engOL 30